Although the automobile or passenger car has long been provided with catalytic converter means in the exhaust system, the exhaust pipes of smaller internal combustion engines have not been significantly modified in respect of pollution reduction. The ceramic monoliths of current design do not well lend themselves to adaptation to the smaller engines. A principal problem with the ceramic monoliths used in catalytic converters is fragility, and the vibration induced by small engines, especially two stroke low horsepower engines, exacerbates this problem. Moreover, ceramic monoliths must be cast or extruded which severely limits design to straight through cells in the monolith. Some of the exhaust lines of small engines are not straight and do not adapt well to cores with an axis that is straight to such designs. The introduction of corrugated thin metal monoliths has overcome the problem of fragility, and enabled design variations to fit the motorcycle exhaust pipe geometry.
The present invention is an improvement in the means for catalyzing oxidation of pollutants, such as, carbon monoxide and unburned hydrocarbons, especially in the exhaust lines of small engines, or engines in which the configuration of the exhaust line does not readily lend itself to the use of ceramic monoliths. It has been found that adequate catalytic conversion of the pollutant materials in the exhaust to environmentally acceptable materials may be inexpensively and effectively achieved by providing a novel insert adapted to fit within the current exhaust line. This insert depends upon a metal oxide coated thin metal strip desirably having a catalyst deposited on or absorbed in the pores of the metal oxide coating. Usually, this coating is alumina applied by wash coating the metal strip and firing to firmly adhere the coating to the metal surface. The thin metal strip may be corrugated. The strip is applied to a metal form either by layering the strip on the surface of the metal form or wrapping the flexible foil about the metal form. The metal form may have any configuration, e.g., a flat plate, or a three dimensional configuration, e.g., a tube of any desired cross-sectional form, e.g., circular, square or triangular. The assembly of the catalyst containing thin metal foil with the metal form is adapted to be inserted within the exhaust pipe and fastened or otherwise secured therein by any suitable means.
Reference may be had to the Cornelison et al U.S. Pat. No. 4,711,009 dated Dec. 8, 1987 for a disclosure of a process for making a corrugated thin metal foil or strip and applying an alumina wash coat and catalyst to the surface thereof. This patent also discloses accordion folding of the corrugated foil, but this operation is not a part of the present invention. This patent is incorporated herein by reference thereto as if the disclosure thereof had been reproduced herein in toto.
U.S. Pat. No. 3,840,471 to Acres dated Oct. 8, 1974 discloses a catalyst useful herein and comprising platinum, rhodium and a base metal, e.g., nickel, cobalt, iron, copper, molybdenum indium, tin, zinc, silver or chromium. A process for applying the catalyst coatings and useful herein, is described in the Stiles U.S. Pat. No. 3,513,109 dated May 19, 1970.